Charette protocol,

The Simmons-Smith cyclopropanation of the same 3-(2-phenylcydopropyl)prop-2-enol (110) in its racemic form afforded an inseparable mixture of and a t/-bicyclopropanes 111 in a 1.3 1 ratio. Therefore, the Charette protocol (p 286) was used first to prepare the required allylic alcohol in its optically pure form and the cyclopropanation was carried out in the presence of the tartrate derived dioxaborolane 93. By using (+)- and (— )-tartrate derived dioxaborolane 93, both the syn- and antf-bicyclopropyls 111 were obtained. The diastereoselectivities observed in their formation were consistently greater than 12 1. ... 

Charette and Brochu have reported an alternate protocol for the Lewis acid-catalyzed cyclopropanation reaction of allylic alcohols, in which the uncatalyzed process is suppressed . The addition of Zn(CH2l)2 (1 equivalent) to an allylic alcohol (1 equivalent)... 

Conversely, Charette and coworkers have shown that the chiral phosphate 23 could be used in catalytic amounts for the cyclopropanation of protected allylic alcohols (equation 97) . This was made possible by using DME as the additive to slow down the background cyclopropanation process, leading to racemic cyclopropane (Pathway A). Bis(iodomethyl)zinc was used as the stoichiometric reagent to regenerate the reactive iodomethylzinc phosphate (Pathway B). Excellent enantioselectivities were observed using this protocol however, the scope of the reaction is still quite limited. 

Charette recently described an innovative activation protocol in which lactams, in the presence of triflic anhydride (33), react with pyridines to afford the pyridinium imidate 107 in good yield. Subsequent addition of metal enolates to this species leads to 2-substituted tricyclic dihydropyridines, advanced intermediates for the total synthesis of the natural alkaloid ( )-tetraponerine T4 (109, Scheme 16) [107]. 

Charette and Brochu have reported an alternative protocol for the Lewis acid-catalyzed cyclopropanation reaction of allylic alcohols, in which the uncatalyzed process is minimized [21]. The addition of Zn(CH2l)2 (1 equiv) to an allylic alcohol (1 equiv) produced the iodomethylzinc alkoxide (Scheme 9). Methylene transfer from these less reactive species is triggered by the addition of a Lewis acid in catalytic amounts. Several achiral Lewis acids such as TiC, SnCl4, and BBr3 were effective in inducing the cyclopropanation. 

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